Loop Cut and Slide in Blender 2.74
It looks like you are using a custom keyboard shortcut preset. The default is called "Blender":



If you reset to factory settings in File > Load Factory Settings does it appear? This won't be permanent unless you save your startup .blend, so you can check to see if it's there without deleting your customized setup.

Also check to see if the operator is there by pressing Space in the 3D view while in edit mode and typing in "loop":